Re: [x86_64 PATCH] PR target/113690: Fix-up MULT REG_EQUAL notes in STV.

[Uros Bizjak <ubizjak@gmail.com>]

On Mon, Feb 5, 2024 at 1:24 AM Roger Sayle <roger@nextmovesoftware.com> wrote:
>
>
> This patch fixes PR target/113690, an ICE-on-valid regression on x86_64
> that exhibits with a specific combination of command line options.  The
> cause is that x86's scalar-to-vector pass converts a chain of instructions
> from TImode to V1TImode, but fails to appropriately update the attached
> REG_EQUAL note.  Given that multiplication isn't supported in V1TImode,
> the REG_NOTE handling code wasn't expecting to see a MULT.  Easily solved
> with additional handling for other binary operators that may potentially
> (in future) have an immediate constant as the second operand that needs
> handling.  For convenience, this code (re)factors the logic to convert
> a TImode constant into a V1TImode constant vector into a subroutine and
> reuses it.
>
> For the record, STV is actually doing something useful in this strange
> testcase,  GCC with -O2 -fno-dce -fno-forward-propagate
> -fno-split-wide-types
> -funroll-loops generates:
>
> foo:    movl    $v, %eax
>         pxor    %xmm0, %xmm0
>         movaps  %xmm0, 48(%rax)
>         movaps  %xmm0, (%rax)
>         movaps  %xmm0, 16(%rax)
>         movaps  %xmm0, 32(%rax)
>         ret
>
> With the addition of -mno-stv (to disable the patched code) it gives:
>
> foo:    movl    $v, %eax
>         movq    $0, 48(%rax)
>         movq    $0, 56(%rax)
>         movq    $0, (%rax)
>         movq    $0, 8(%rax)
>         movq    $0, 16(%rax)
>         movq    $0, 24(%rax)
>         movq    $0, 32(%rax)
>         movq    $0, 40(%rax)
>         ret
>
>
> This patch has been tested on x86_64-pc-linux-gnu with make bootstrap
> and make -k check, both with and without --target_board=unix{-m32}
> with no new failures.  Ok for mainline?
>
>
> 2024-02-05  Roger Sayle  <roger@nextmovesoftware.com>
>
> gcc/ChangeLog
>         PR target/113690
>         * config/i386/i386-features.cc (timode_convert_cst): New helper
>         function to convert a TImode CONST_SCALAR_INT_P to a V1TImode
>         CONST_VECTOR.
>         (timode_scalar_chain::convert_op): Use timode_convert_cst.
>         (timode_scalar_chain::convert_insn): If a REG_EQUAL note contains
>         a binary operator where the second operand is an immediate integer
>         constant, convert it to V1TImode using timode_convert_cst.
>         Use timode_convert_cst.
>
> gcc/testsuite/ChangeLog
>         PR target/113690
>         * gcc.target/i386/pr113690.c: New test case.

OK.

Thanks,
Uros.

>
>
> Thanks in advance,
> Roger
> --
>